The present invention relates to an electron-beam irradiation system and an electron-beam irradiation method which are used, for example, for recording on a master of optical disks.
In recent years, as to optical disks, there has been a demand for a higher recording density and, for this purpose, it is necessary to form recording pits more finely.
In the manufacture of a master for optical disks, therefore, a system for recording by irradiating the master with an electron-beam in place of a conventional laser light has been proposed.
In such an electron-beam irradiation system, irradiation with the electron-beam in a vacuum environment is required to obviate the problem that the electron-beam is scattered due to its collision with gas molecules.
In this case, if the entire body of the electron-beam irradiation system is placed in a vacuum environment, a large vacuum space and a large-type exhaust means are required, so that the system becomes large in size and high in cost.
To obviate this problem, the present applicant has proposed, in Japanese Patent Application No. 2000-57374, a oartial-vacuum-type, electron-beam irradiation system in which only the portion for irradiation with the electron-beam is placed in a vacuum state.
Namely, in this electron-beam irradiation system, a static-pressure floating pad is connected to an electron-beam outlet of a vacuum chamber in which an electron-beam column is incorporated, the static-pressure floating pad is contactlessly attracted to a master with a small gap of about several micrometers under suction by an exhaust means and supply of a compressed gas by a gas-supply means, and, in this condition, an electron-beam emitted from an electron gun passes through an electron-beam passage at a central portion of the static-pressure floating pad to impinge upon the master.
In the electron-beam irradiation system, as above, the operation of exchanging the master makes it necessary to retract the static-pressure floating pad from the master.
In this case, the static-pressure floating pad is separated completely from the master, so that the atmospheric air flows into the inside of the vacuum chamber through the electron-beam passage of the static-pressure floating pad, and the electron-beam column is exposed to the atmospheric air.
Therefore, it is necessary to protect the electron gun by closing a gate valve of the electron-beam column while the high vacuum before the retraction of the static-pressure floating pad is maintained and the exhaust means (vacuum pump) for providing vacuum in the vacuum chamber by turning OFF the power source thereof; thus, workability is very poor.
Besides, in the case of starting up the vacuum system again after the exchange of the master, several hours is taken for the degree of vacuum in the vacuum chamber to be raised to a level suitable for irradiation with the electron-beam and to be stabilized. Thus, the system is very poor in efficiency in that the waiting time is longer than the time required for recording on the master by irradiation with the electron-beam.
Further, since the inside of the vacuum chamber is opened to the atmospheric air each time the master is exchanged, there is the problem of contamination of the insides of the vacuum chamber and the electron-beam column due to taking in dust from the atmospheric air.
The present invention has been made in consideration of the above-mentioned problems, and, accordingly, it is an object of the present invention to solve the above-mentioned problems by making it possible to maintain a desired degree of vacuum in the vacuum chamber even where the static-pressure floating pad is separated from the body to be irradiated (original disk) in the oartial-vacuum-type electron-beam irradiation system.
In order to attain the above object, according to the aspect of the present invention, there is provided an electron-beam irradiation system including an electron-beam column, a vacuum chamber incorporating the electron-beam column and a static-pressure floating pad connected to the vacuum chamber wherein an electron-beam passes through an electron-beam passage to impinge on a body to be irradiated in the condition where the static-pressure floating pad is contactlessly attracted to the body to be irradiated. The electron-beam irradiation system also includes a vacuum-seal valve for opening and closing the electron-beam passage, the vacuum-seal valve being provided in the inside of the static-pressure floating pad.
According to another aspect of the present invention, there is provided an electron-beam irradiation method using an electron-beam irradiation system including an electron-beam column, a vacuum chamber incorporating the electron-beam column, and a static-pressure floating pad connected to the vacuum chamber, wherein an electron-beam passes through an electron-beam passage to impinge on a body to be irradiated in the condition where the static-pressure floating pad is contactlessly attracted to the body to be irradiated. The electron-beam irradiation method includes the step of moving a vacuum-seal valve that is movably disposed in the inside of the static-pressure floating pad to close the electron-beam passage, and thereby the inside of the vacuum chamber is maintained at a desired degree of vacuum.
In the electron-beam irradiation system and method according to the present invention constituted as above, the electron-beam passage is closed by operating the vacuum-seal valve when the static-pressure floating pad is separated from the body to be irradiated, whereby the atmospheric air is prevented from flowing into the vacuum chamber through the electron-beam passage, and the inside of the electron-beam column can be maintained at a degree of vacuum substantially suitable for irradiation with the electron-beam.
Therefore, according to the invention, it is unneccessary to protect the electron gun by closing the gate valve of the electron-beam column and turning OFF the power source of the exhaust means for the vacuum chamber each time when the static-pressure floating pad is separated from the body to be irradiated, as in the related art. Thus, the operation is simplified and operation time is shortened, namely, workability is enhanced. In addition, since the inside of the vacuum chamber can be maintained in a vacuum condition, contamination of the insides of the vacuum chamber and the electron-beam column can be prevented.
The above and other objects, features and advantages of the present invention will become apparent from the following description and appended claims taken in conjunction with the accompanying drawings which show by way of example some preferred embodiments of the invention.